Improvements relating to hydrophones

ABSTRACT

A hydrophone adapted to be suspended underwater by means of a cable, which preferably carries electrical leads as cores thereof, includes a transducer element having substantially axial symmetry. The element is secured in a yoke by means of mountings positioned on the axis of symmetry, and the electrical leads for deriving output signals from the element are connected to respective points on the transducer so that the effects of vibrations transmitted along the cable to the element tend to be self-cancelling.

ited States Patent 1191 Bennett [54] IMPROVEMENTS RELATING TO HYDROPHONES [75] Inventor: Derek J. Bennett, Bedford, Nova Scotia, Canada [73] Assignee: EMI Limited, Middle sex, England 221 Filed: April 22,1970

21 Appl.No.:30,924

[30] Foreign Application Priority Data [581' Field oi Search ..340/8, 10,13, 7, ll; 3l0/9.l

[ 1March 20, 1973 [56] References Cited UNITED STATES PATENTS 3,489,994 1/1970 Massa ..340/22 R 2,728,901 12/1955 Millen ..340/8 MM Primary -Examiner--Benjamin A; Borchelt Assistant Examiner-R. Kinberg Att0rney-Fleit, Gipple & Jacobson [5 7 ABSTRACT A hydrophone adapted to be suspended underwater by means of a cable, which preferably carries electrical leads as cores thereof, includes a transducer element having substantially axial symmetry. The element is secured in a yoke by means of mountings positioned on the axis of symmetry, and the electrical leads for deriving output signals from the element are connected to respective points on the transducer so that-the effects of vibrations transmitted along the cable vto the element tend to be self-cancelling.

3 Claims, 2 Drawing Figures PATENTEDmzoms 3,721,853

MENTOR 'DEREK 'BEMN IMPROVEMENTS RELATING TO I-IYDROPI-IONES This invention relates to hydrophones. I

A known form of hydrophone includes a cylindrical piezo-ceramic transducer element, which can be suspended in water by means of a cable. When such a hydrophone is suspended in water, noise tends tobe in-' duced in the output of thehydrophonewhen the flow of water causes strumming acceleration forces along the suspending cable.

The object of the present invention is to provide an sockets and apertures, securing the assembly in the yoke.

In order that the present invention may be clearly understood and readily carried into effect it will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of a hydrophone according to one example of the invention,

FIG. 2 is an end view of the hydrophone illustrated in FIG. 1.

Referring to the drawing, the hydrophone comprises a piezo-ceramic transducer element in the form of a hollow cylinder 1 which is held between two circular end caps 2 and 3. The caps 2 and 3 each include a central axially extending socket, and the transducer element 1 and caps 2 and 3, except for the aforementioned sockets are covered witha waterproof insulating jacket 6 to form a transducer assembly. The mount for the transducer assembly comprises a yoke 4 to which the assembly is secured by two screws 5 which pass through apertures of the yoke and are screwed into the sockets of caps 2 and 3. As illustrated, the sockets by means of which the transducer assembly is secured to the yoke, lie at opposite ends of the axis of symmetry of the cylindrical transducer element 1. The hydrophone can .be suspended in water by'imeans of a cable 8 .carry-' ing the leads 9 and 10 which are secured as indicated to the inner and outer surfaces of the piezo-ceramic element 1. The cable 8 is anchored to the yoke 4 at the point 7 by means of an anchoring loop, of cord for example.

When a hydrophone of the construction illustrated is subject to acceleration force in any radial direction two opposite and substantially cancelling voltages are generated, one is due to compression force occurring on one side of the element and the other to tensile force occurring on the other side. Similarly when the hydrophone is subjectto an acceleration force in the axial direction two opposing and substantially cancelling voltages are generated due respectively to compression at one end of the element and tension at the other. In the example of the invention described, the

element 1 is suspended with its axis horizontal, and it has been found by experiment that this mode of suspension renders the hydrophone least sensitive to acceleration. However a substantial reduction in acceleration noise occurs for any orientation of the element. For an element formed of a short piezo-ceramic cylinder having a length to diameter ratio of one half and suspended with its axis horizontal, a reduction in acceleration sensitivity of 40dB was achieved compared with a similar element suspended without a yoke.

' What I claim is:

l. A hydrophone comprising a transducer assembly including a substantially cylindrical, annular transducer element, two substantially circular end caps closing respective ends thereof, each of the caps having a central, outwardly facing socket, and a waterproof insulating jacket surrounding the element and the end caps, the sockets however being uncovered, a rigid yoke provided with apertures adapted to co-operate with the sockets of the assembly, and means, utilizing said sockets and apertures, securing the assembly in the yoke..

2. A hydrophone according to claim 1 wherein one end cap, the jacket and yoke are provided with apertures, and a cable is threaded through the apertures, the cable beingsealed in watertight manner to said jacket and wherein respective mutually insulated electrically conductive cores of said cable are connected to the transducer element for deriving output signals therefrom, the cable being clamped externally to the yoke.

3. A hydrophone according to claim 2 wherein, in operation, the cable is so clamped to the yoke that the hydrophone is suspended with the axis of symmetry of said element substantially horizontal.

' II t t i 

1. A hydrophone comprising a transducer assembly including a substantially cylindrical, annular transducer element, two substantially circular end caps closing respective ends thereof, each of the caps having a central, outwardly facing socket, and a waterproof insulating jacket surrounding the element and the end caps, the sockets however being uncovered, a rigid yoke provided with apertures adapted to co-operate with the sockets of the assembly, and means, utilizing said sockets and apertures, securing the assembly in the yoke.
 2. A hydrophone according to claim 1 wherein one end cap, the jacket and yoke are provided with apertures, and a cable is threaded through the apertures, the cable being sealed in watertight manner to said jacket and wherein respective mutually insulated electrically conductive cores of said cable are connected to the transducer element for deriving output signals therefrom, the cable being clamped externally to the yoke.
 3. A hydrophone according to claim 2 wherein, in operation, the cable is so clamped to the yoke that the hydrophone is suspended with the axis of symmetry of said element substantially horizontal. 